I had only one key for my X5 so purchased a blank , had it cut , purchased another working BMW key and swapped the innards.
Programmed it - 'hold UNLOCK and press LOCK key 3 times ' repeat with new key etc .
I now have a spare key that will unlock and lock the doors either manually or remotely , it will turn on the ignition but then the immobiliser will not let me crank the engine !
However if I start the engine with the original key , turn it off and insert the new key it will let me start the engine as often as I want until I open and close the door and then it won't turn the engine over again !
Not a lot of good as a spare key if I need the original to make it work LOL.

Anyone any ideas ?